b 1. Field of the Invention
The present invention relates to an internal combustion engine intended to reduce the harmful exhaust gases which have been public problems in recent years and, more particularly, to a so-called "stratified internal combustion engine" in which the combustion of an air-fuel mixture, which is lean as a whole, is achieved by holding an ignitable rich air-fuel mixture in the vicinity of a spark plug to thereby assure the purification of the exhaust gases.
2. Description of the Prior Art
As a stratified internal combustion engine intended for the purification of exhaust gases, an engine has been proposed which is of the type that has a combustion chamber formed by a main combustion chamber and a trap chamber having a spark plug disposed therein, and an intake system comprising a lean mixture supply means for supplying a relatively lean air-fuel mixture to the main combustion chamber and a rich mixture supply means for supplying a relatively rich air-fuel mixture to the trap chamber. The total of the lean and rich air-fuel mixture is lean as a whole, but the rich mixture introduced into and held in the trap chamber is ignitable by a spark plug.
In general, in this type of internal combustion engine, assuming that the air-fuel ratio of the total of the lean and rich air-fuel mixture is fixed, if the air-fuel ratio of the rich air-fuel mixture supplied by the rich mixture supply means is determined to be small, the air-fuel mixture present in the trap chamber just before the mixture is ignited by the spark plug can be rich accordingly. Thus, it is advantageous to enrich the air-fuel mixture for the trap chamber as far as the stratification of the mixtures is concerned. However, because the atomization of the fuel becomes poor as the air-fuel ratio of the air-fuel mixture is made smaller (enrichment of the mixture), it is disadvantageous to enrich the air-fuel mixture in the trap chamber as far as the atomization of the fuel is concerned. In order to realize the purification of exhaust gases by the achievement of certain stratified combustion, appropriate air-fuel ratios should be determined for the lean and rich air-fuel mixtures.
As the lean and rich mixture supply means, either an air-fuel intake system including carburetors or a fuel injection system including fuel injection nozzles has conventionally been employed. In either case, different carburetors or fuel injection nozzles have been used for lean and rich air-fuel mixtures, respectively. This is partly because a carburetor or fuel injection nozzles are naturally required for the rich air-fuel mixture and partly because the substitution of air for the lean air-fuel mixture is disadvantageous to the purification of exhaust gases for the above reason and, thus, a carburetor or fuel injection nozzles have been needed for the lean air-fuel mixture.
It will be apparent that the installation of different carburetors or fuel injection nozzles for the lean and rich air-fuel mixtures, respectively, increases the cost of manufacture and makes the engine construction complicated.